Photovoltaic devices such as solar cells are known in the art. A solar cell may include, for example, a photoelectric transfer film made up of one or more layers located between a pair of substrates or other layers. These layers may be supported by a glass substrate. Example solar cells are disclosed in U.S. Pat. Nos. 4,510,344, 4,806,436, 6,506,622, 5,977,477, and JP 07-122764, the disclosures of which are hereby incorporated herein by reference.
Substrates in solar cells (or photovoltaic devices) are sometimes made of glass. Glass that is fairly clear in color and highly transmissive to visible light is sometimes desirable. Glass raw materials (e.g., silica sand, soda ash, dolomite, and/or limestone) typically include certain impurities such as iron, which is a colorant. The total amount of iron present in glass is expressed herein in terms of Fe2O3 in accordance with standard practice. However, typically, not all iron is in the form of Fe2O3. Instead, iron is usually present in both the ferrous state (Fe2+; expressed herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO) and the ferric state (Fe3+). Iron in the ferrous state (Fe2+; FeO) is a blue-green colorant, while iron in the ferric state (Fe3+) is a yellow-green colorant. The blue-green colorant of ferrous iron (Fe2+; FeO) is of particular concern when seeking to achieve a fairly clear or neutral colored glass, since as a strong colorant it introduces significant color into the glass. While iron in the ferric state (Fe3+) is also a colorant, it is of less concern when seeking to achieve a glass fairly clear in color since iron in the ferric state tends to be weaker as a colorant than its ferrous state counterpart.
Higher transmission through light incident flat glass substrates of photovoltaic devices has been achieved by lowering the levels of impurities in the glass, especially iron, that contribute to the absorption of energy. In this regard, it has been found that the use of a low-iron highly transparent glass is advantageous for solar cell applications. However, it would be desirable if visible transmission could be further increased, thereby permitting photovoltaic devices to be even more efficient in the generation of electrical current from sunlight.
Thus, it will be appreciated that there exists a need in the art for a high transmission glass structure for use in electronic devices such as photovoltaic devices, where the glass structure is capable of allowing much solar radiation to pass there through. At the same time, it would also be desirable if the glass structure could be designed such that seals/casings could efficiently and securely be attached to the electronic device in order to adequately protect the same from mechanical damage and/or environmental conditions.
Transmission of solar radiation (UV, visible and/or IR) through a glass substrate can be increased by reducing the approximately 4% of light that is reflected off of the flat top surface of a light-incident side glass substrate of a photovoltaic device. One technique for further achieving such a reduction in reflectance (and thus achieving an increase in transmission by reducing reflection) is to use a patterned glass substrate on the light-incident side of the photovoltaic device. A patterned or heavily textured glass as a light-incident side glass substrate of a photovoltaic device may have geometric features such as cones, pyramids, and/or ridges formed in the light-incident surface of the glass substrate which are designed to recapture reflected light so as to increase the transmission of light through the glass substrate toward the semiconductor absorber. Such patterns are especially effective at capturing so called off-axis light, e.g., that which is present in the early morning and/or late afternoon situations, thereby increasing the efficiency of the device.
Thus, the use of a low-iron glass composition in combination with a patterned major surface of the light-incident glass substrate has been found to be advantageous with respect to optical properties, thereby leading to increased solar efficiency of photovoltaic devices such as solar cells. In photovoltaic devices, it is generally desirable for the glass substrate on the light-incident side of the semiconductor film (sometimes referred to as the semiconductor absorber) to allow as much radiation as possible (UV, IR and visible) to pass therethrough so that the photoelectric semiconductor transfer film (or semiconductor absorber) of the device can convert the radiation to as much current as possible. The less radiation allowed to pass through the glass substrate, the less current generated in the photovoltaic device.
In certain example embodiments of this invention, the major surface of the glass substrate on the light-incident side of the electronic device (e.g., photovoltaic device) is ground down so as to be substantially flat at edge portion(s) of the patterned side of the glass. In certain example embodiments, this grinding may be performed only at or proximate edge portions of the glass substrate (i.e., not in central portions of the light-incident glass substrate). The ground portions proximate the edge portion(s) of the glass are advantageous, for example, in that a frame (e.g., metal frame) can more easily fit around the edge(s) of the electronic device so as to at least partially encapsulate the device. Such frames are provided around the edges of photovoltaic devices, for instance, in order to protect the edges from mechanical damage and/or to seal the edges against ingress of water and the like. The ground-flat portions may be provided around the entire periphery of the glass substrate (e.g., at or proximate edge portions along all four sides of a rectangular substrate) in certain example instances, or alternatively around only one, two or three sides of the glass substrate in alternative instances, according to different embodiments of this invention.
In certain example embodiments of this invention, there is provided a photovoltaic device comprising: a glass substrate, a front electrode, and a photoelectric film, where the front electrode is provided between at least the glass substrate and the photoelectric film; the glass substrate having first and second major surfaces, with at least part of the first major surface of the glass substrate being patterned and located at a light-incident side of the glass substrate so that light incident on the photovoltaic device hits the first major surface of the glass substrate before hitting the second major surface of the glass substrate; wherein at least a central portion of the first major surface of the glass substrate is patterned so as to define a plurality of peaks and valleys in a patterned portion; a frame encapsulating at least part of an edge of the photovoltaic device so as to protect the at least part of the edge of the photovoltaic device from damage; and wherein an edge portion of the first major surface of the glass substrate, immediately adjacent an absolute edge of the glass substrate, is substantially flat and is located immediately adjacent the peaks and/or valleys of the patterned portion on the same first major surface, and wherein part of the frame is located over the substantially flat edge portion but not over the patterned portion of the first major surface of the glass substrate.
In other example embodiments of this invention, there is provided a glass substrate for use in an electronic device, the glass substrate comprising: the glass substrate having first and second major surfaces, with at least part of the first major surface of the glass substrate being patterned and located at a light-incident side of the glass substrate so that light incident on the photovoltaic device hits the first major surface of the glass substrate before hitting the second major surface of the glass substrate; wherein at least a central portion of the first major surface of the glass substrate is patterned so as to define a plurality of peaks and valleys in a patterned portion; and wherein an edge portion of the first major surface of the glass substrate, immediately adjacent an absolute edge of the glass substrate, is substantially flat and is located immediately adjacent the peaks and/or valleys of the patterned portion on the same first major surface, the substantially flat edge portion of the glass substrate being adapted to be at least partially covered by a frame such that the frame does not cover any significant part of the patterned portion of the first major surface of the glass substrate.
In still further example embodiments of this invention, there is provided a method of making a photovoltaic device, the method comprising: providing a glass substrate having first and second major surfaces, wherein the first major surface of the glass substrate is patterned so as to define a plurality of peaks and valleys in a patterned portion; grinding down an edge portion of the first major surface of the glass substrate, using at least one grinding wheel, so as to grind the patterned portion substantially flat at the edge portion but not in a central portion of the first major surface of the glass substrate, wherein following said grinding the edge portion is substantially flat; forming the photovoltaic device so that the glass substrate is located at a light-incident side of the photovoltaic device, and the second major surface of the glass substrate is closer to a semiconductor film of the photovoltaic device than is the first major surface which includes both the patterned portion and the substantially flat edge portion; and attaching a frame to the photovoltaic device so that the frame at least partially covers the substantially flat edge portion of the first major surface of the glass substrate but does not cover the patterned portion of the first major surface of the glass substrate.